In general, an optical receptacle is an optical device that accepts an optical fiber connector to connect to another optical device, such as a laser diode, a photodetector, or another optical fiber. Optical connectors are standardized in order to fit into receptacles from different manufacturers. Common standards are for example SC-connectors and LC-connectors.
Optical input to and output from an optical device is passed through the receptacle, which is connected to the device. When light is launched into or taken out from an optical fiber, it is passed through a refractive index boundary. A refractive index boundary is also a requisite for refracting the light, for the purpose of collimating or focusing.
At the mating end (the end which is to be inserted into a receptacle) of a fiber connector, there is typically arranged a ferrule in which the fiber is fitted. This ferrule is inserted into the optical receptacle in order to connect the fiber therein to the optical device connected to the receptacle.
In order to reduce back-reflections, the tip of the mating fibre is generally anti-reflection coated or angle-cut. In some configurations an optical insulator, which is a rather bulky device, is employed. Requirements are put on both the connector and on the receptacle in order to provide good optical throughput to or from an optical device, and to minimize back-reflections from the fiber end. However, the fiber connector and the receptacle are generally not manufactured by the same manufacturer. Since the degree of optical throughput is dependent on both the quality of the connector and the quality of the receptacle, the manufacturer of the receptacle thus cannot guarantee certain specifications of optical throughput irrespective of the type of connector used and the quality of the mating fiber.
The degree of optical throughput also depends on the interface between the receptacle and the optical device arranged at the back end thereof, to which the mating fiber is to be optically connected by means of the receptacle. Any disturbances of the position of a laser or a photodetector relative to the receptacle will result in a degradation of the optical throughput.
U.S. Pat. Nos. 6,071,016 and 5,617,495 are two examples of prior art optical receptacle solutions which address these problems.
In U.S. Pat. No. 6,071,016 a fiber stub is held by a sleeve and optically coupled to the mating optical fiber for connection. In this way, the nature of the refractive index step is determined by the end tip of the fiber stub, and not by the characteristics of the mating fiber. A lens on the back side of the fiber stub guides the incoming light to a photodetector unit. This increases the optical throughput, since the light can be focused directly to the active area on the photodetector. However, it is still very important that no misalignments occur between the receptacle unit and the photodetector, since the optical throughput will be drastically reduced if the focused light beam is not perfectly matched with the active area of the photodetector.
In U.S. Pat. No. 5,617,495 a short optical fiber has one end (a “pig tail”) optically connected to a laser diode, and an opposite end housed in a ferrule, which is inserted into and fixed to a sleeve that is mounted in a module package. The mating fiber is optically coupled to this short optical fiber when the connector is connected. In this way, accurate alignment of the receptacle and the optical device is possible. However, the receptacle and the optical device have to be joined at assembly. It is not possible to manufacture the optical package and the receptacle separately, which may be desired.
Hence, there is a need for new optical receptacle solutions.